The present invention relates in general to combination locks, and more particularly to combination locks especially designed to resist compromise of security by detection of the opening combination of the lock through radiography or high energy radiation techniques.
Locks of the type commonly referred to as combination locks depend for their operation upon the alignment of a plurality of disc-like rotary elements, commonly called tumbler wheels, in a preselected manner to permit retraction of a reciprocative bolt from its projected position. Each tumbler is provided with a peripheral recess, commonly termed a gate, designed to receive a bar or fence normally disposed in overlying relation with the tumbler wheel peripheries and extending from a fence lever which is pivoted or otherwise coupled to a bolt and controls movement of the latter. When the tumbler gates are all disposed in registry with each other and in preselected alignment with the fence, and a driving cam which effects angular adjustment of the tumbler wheels through lost-motion connections and controls the fence lever is adjusted to a selected angular position, the fence may drop into the tumbler gates and permit such an interconnection of the fence lever with the driving cam that limited arcuate movement of the driving cam will impart movement to the fence lever to retract the bolt. The security of such locks is dependent upon the fact that the number of orders or permutations of the possible relative positions of the tumbler gates before all of the tumbler gates come into registry with the fence to permit retraction of the bolt is so large that the chance of these gates being aligned by a person not familiar with the combination is negligible.
In recent years, mechanical arrangements have been devised which are reasonably effective to protect the combination lock against mechanical manipulation thereof by unauthorized persons to surreptitiously detect the combination. However, various techniques have been developed in recent years for compromising the security of combination locks in safes and other security closures by the use of high-energy radiation. These have been variously termed radiography or radiological techniques and in general involve the production of pictures or other types of images of the lock works by photographing high-energy radiation which has passed through the lock mechanism, or by oterwise measuring such radiation emerging at various locations or for various positions of the pack of tumbler wheels. With the developments made in portable radiation sources, unauthorized persons may enter on the premises containing a security container and by radiological methods determine the combination setting of the lock and secure unauthorized entry to the protected enclosure in a short time without leaving any evidence of compromise of the lock combination.
Various arrangements have been devised in an effort to protect combination locks against compromise of the combination by such radiographic techniques, including particularly the provision of radiant energy scattering devices disposed within the lock housing, especially in surrounding relation to the tumbler wheels, to effect scattering of the penetrating radiation and thereby confound the image or photograph produced by radiological techniques. Examples of such radiant energy scattering devices may be found in earlier U.S. Pat. Nos. 2,970,217 and 3,024,640.
Other efforts to avoid detection by such radiographic image techniques attempting to permit observation of the angular locations of the tumbler wheel gates, with or without the presence of such radiation scattering devices, has been to form the tumbler wheels of low density materials such as nylon, rather than the metallic materials conventionally employed, to minimize the production of X-ray or high energy radiation shadows which would reveal the positions of the tumbler wheel gates.
In addition to use of X-ray photography techniques which provide a flat photograph of the wheel pack showing the positions of the gates, neutron beam gauging techniques or related high energy radiation measuring techniques have also been developed to reveal the combination of the lock. In the neutron beam gauging procedure, a neutron beam from an appropriate source is aimed at the edge of the tumbler wheel pack and the location of the gates is indicated on a counting device by a higher count for a set time period, which results from less metal, nylon or other material from which the tumbler wheel is made being in the beam path when the beam passes through a gate.
Some of the techniques developed to attempt to resist attack by such radiation detection procedures have included provision of additional false gates on each of the tumblers in addition to the true gate, to confound the radiological image, or the use of additional false tumbler wheels which indicate additional combination positions other than those for the true gates of the true tumbler wheels. Another technique developed is that disclosed in the Todd U.S. Pat. No. 3,983,727 of Oct. 5, 1976 assigned to the United States of America as represented by the Secretary of the Army, wherein a wheel pack is used in which a novel true-false gate system is provided on the perimeters of the tumbler wheels. The tumbler wheels are provided with a large number of gates about the periphery of each tumbler wheel, the gates being cut in the shape of right triangles and so positioned that the hypotenuse of the triangle on one side of each wheel intersects the hypotenuse of the triangle on the other side of the wheel, and only one of the gates on each wheel is a true gate. The contact portion of the fence associated with these tumbler wheels is designed to only contact one-half of each wheel and is shaped so that it will only fit into a gate whose shape and orientation is identical to the fence. Since all of the gates, whether true or false, have a mirror image gate immediately behind them, they all look the same in the X-ray image or the neutron counter measurement.
While combination locks with the Todd type tumbler wheel construction are effective in resisting radiological detection, the tumbler wheels disclosed in that patent are not of a construction suitable for effecting change of the lock combination. Obviously periodic changing of the combination of the lock by security personnel is a useful and important additional factor in deterring unauthorized opening of the combination lock.
An object of the present invention, therefore, is the provision of a novel combination lock with tumbler wheels having hub portions or wheel centers and rim portions or wheel cases, capable of being changed in their relative angular positions to each other circumferentially of each tumbler wheel to change the lock combination, and wherein the tumbler wheel gate arrangement provides true and false gates resistant to radiation detection, and the tumbler wheels are not provided with any change key holes in the wheel or gate configurations which could be detected radiographically.
Another object of the present invention is the provision of a novel radiographic detection resistant combination lock construction as described in the immediately preceding paragraph, wherein novel means are provided to effect axial movement of the wheel centers or hub portions of the tumbler wheels making up the wheel pack is effected by means which avoid the use of a change key which would require change key holes in the tumbler wheel centers or hub portions to resist radiographic detection of tumbler wheel position by detection of key change wheel openings.
Still another object of the present invention is the provision of such a combination lock construction wherein novel means are provided to restrain the tumbler wheel cases or rim portions against movement during combination change movement of the tumbler wheel centers or hub portions without revealing the position of the true gates of the tumbler wheels.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating preferred embodiments of the invention.